This invention relates to insulation material, particularly insulation material suitable for the coils of large rotating electric plant.
Conventionally, large motors, especially those operating at 3.3 KV and higher voltages, have so-called "circumferential" or "diamond" coils comprising shaped turns of conductor, connected by "overhang" sections. The slot-fitting sections must be well insulated. This is conventionally done by wrapping the sections in one of a number of different insulating materials, usually containing mica. The mica may be in the form of particles carried in a resin. There are two basic techniques, one, "resin-rich", being essentially based on such mica paper; the other, so-called vacuum pressure impregnation (VPI), involving impregnating the insulation once on the coil (or even on the coils once on the stator) with a resin. The resin is distributed uniformly around the coil by heat, as by a hot pressing, shaping operation on the coil in a coil press.
The insulating material conventionally comprises a tape, which is wound helically on to the straight, slot-fitting sections of the coil.